Searching for oil or, more generally, hydrocarbons has become more demanding in terms of hardware and devices in recent years because oil and gas fields or reservoirs are located deeper under the earth's surface or in places difficult to reach. Prospecting for and exploitation of hydrocarbon fields demands hardware which can withstand higher loads and ensures optimal sealability. The market for so-called premium connections is increasing and research is being carried out to offer new improved joints to meet market needs.
A primary design requirement for threaded joints is to resist high load torques to ensure that during drilling or running operations, the joint does not fail due to over-torque (i.e. to resist higher torques than connections of similar materials and wall thickness/geometry). However designing joints having good resistance to high loads generally means that high torques are required during make-up operations, at least in the last part of the make-up operation, just before the abutment shoulder is energized with danger of plastic deformation of the metal in the joint portions. In this part of the make-up there is also the danger of causing galling between sealing surfaces.
Attempts have been made to improve joint capacity to achieve a reduced make-up torque combined with high resistance to breakout, as well as to achieve a connection that can be made up with no rotation of the tubular sections, but by rotating only the coupling.
U.S. Pat. No. 5,794,985 discloses a threaded pipe connection for connecting two segments of pipe having externally threaded pin members, one pin member having external right-hand threads and the other pin member having left-hand threads. An internally threaded coupling has two portions having respectively right and left-hand threads that mate with the threading on the respective pin members. A plurality of mating lugs and grooves on the ends of the pin members hold the pins from relative rotation when the connection is being made up. Making up the coupling in the last part of the operation causes a translation of the pins parallel to their axis in mutually opposite directions so that the lugs of the pin extremities enter one into another and prevent rotation of one pin relative to the other. A metal-to-metal seal located between each pin member and the coupling adjacent each end of the coupling isolates the threads of the connection from the ambient environment, thus sealing the pipe annulus against external pressure due to hydrostatic head.
U.S. Patent Application Publication No. 2006/0273586 discloses a threaded joint comprising a first pin nose comprising a nose surface, a shoulder and a seal surface therebetween, a second pin nose comprising a nose surface, a shoulder and a seal surface corresponding to the first pin seal surface, and a mating coupling with an inner seal support. Upon a determined make-up the first pin nose is in an overlapping axial position with the second pin nose such that contact occurs between the first pin nose surface and the second pin shoulder surface acting as a positive-stop torque shoulder, with contact occurring between the first pin seal surface and the second pin seal surface, to form a seal therebetween. The inner seal support is in an overlapping axial position to the first pin nose and the second pin nose, with a selected diametrical gap existing between the inner seal support and the first pin nose and second pin nose.
The threaded joint can be made-up with substantially no relative rotation between the first and second tubular sections. One among the first pin nose surface and the second pin nose surface is castellated, in a similar fashion to a slotted nut, with the corresponding second pin nose shoulder or first pin nose shoulder being correspondingly castellated.
To finish connection make-up, both tubular sections may be restrained from rotating relative to each other while the coupling is rotated. The different thread pitches cause the pin noses to be brought together axially without relative rotation between the tubular sections. Torque continues to be applied to the coupling until the selected make-up is achieved.
The solution proposed by U.S. Pat. No. 5,794,985 relates to threaded pipe connections with thread designs having one pin with left hand threaded end and the second pin with right hand threaded end, where both have the same pitch and taper.
The solution provided by U.S. Patent Application Publication No. 2006/0273586relates to threaded pipe connections having both threads with the same hand but different pitches, and a coupling with a seal inner support having a gap between said inner support and the interlocking pin noses.
Both solutions cited above are unsatisfactory because some problems remain unsolved. A first problem is handling fragility due to the castellated pin ends and inner seal support. In fact if a lug or a groove of a castellated pin end is hit and bent during the handling of the pipe in the yard, the make-up will be much more difficult, with the risk of cross threading and galling increasing dramatically. It may also harm the internal flush or drift.
Another problem relates to manufacturing, because the lugs and grooves, as well as the inner seal support, have to be machined with very precise tolerances, increasing the cost of the connection and the time needed to machine it. Moreover it is technically complicated to cut a right handed thread and a left handed thread at the same time. It is impractical from the cost aspect.
Still another problem is encountered during joint make-up in both solutions of the state of the art. First of all there is a danger of galling the seal surfaces, and plastic deformation of the pin noses, seal surfaces or shoulder surfaces during make-up of the connection. There is a need for a high make-up torque to achieve a good resistance to high working loads, which enhances the risk of the aforementioned problems.
Moreover, to make-up the castellated pin ends, a very good alignment of the mating lugs and grooves from both pin ends and from the coupling is needed.
U.S. Pat. No. 4,762,344 discloses a connection with one of the pipe ends having threads of a pitch that is greater than the pitch of the threads on the other pipe end, and the connector threads have corresponding thread pitches. The disclosed arrangement permits the connection to be assembled to the point short of relative sliding movement between the complementary sealing surfaces on the pipe ends and final tightening is accomplished by restraining the respective pipes from relative rotation while rotating the connector to draw the two pipe ends together into compressive sealing engagement without relative sliding in order to prevent galling of the sealing surfaces. The inclined frustoconical end surfaces of both pipe sections have their virtual vertex lying on the pipe axis. The inclination of each of the frustoconical end surfaces is such that they are obliquely positioned in the same orientation relative to the pipe axes. The angles of the frustoconical end surfaces are slightly different by an angular value of 2° to 5°, to cause the pipe ends, or the pipe ends and the metallic annular sealing rings, depending upon the embodiment being considered, to first make contact at inner edges when the ends are drawn together. Thus the resulting seal commences at the innermost part of the junction and progresses to the exterior of the junction as the axial pressure between the pipe ends increases by virtue of the continued rotation of connector to draw the pipe ends together.